Ultra high frequency control system



S. KRASIK ULTRA-HIGH FREQUENCY CONTROL SYSTEM Filed Jan. 14, 1944 Dec. 17, 1.946.

- WITNESSES:

INVENTOR Sidney Krasz'lr.

ATTORN E Patented Dec. 17, 1946.

ULTRA HIGH FREQUENCY CONTROL SYSTEM Sidney Krasik, Westinghouse burgh, Pa, a corpora Wilkinsburg, Pa., assignor to Electric Corporation, East Pittstion of Pennsylvania Application January 14,1944, Serial No. 51 ,222-

This invention relates to an ultra-high frequency electrical system and has articular relation to apparatus for controlling the transmission of energy through the electromagnetic energy transmission lines of such a system.

In ultra-high frequency circuits including transmission lines, comprising guides for electromagnetic waves, such as coaxial lines or hollow Wave guides, it is frequently desirable to effect switching or tuning of the circuits. Prior art arrangements for accomplishing such switching or tuning comprise mechanically-operated tuning screws, plugs, irises, attenuators, and similar de vices. In these arrangements, the device is designed to effect a mechanical change within the wave guide to change the electrical properties of the line. In addition to the manufacturing problems involved in the prior art devices, remote control of the devices is rather difficult.

It is, accordingly, an object of my invention to provide a new and improved apparatus for tuning or switching an ultra-high frequency circui Another object of my invention is to provide a novel apparatus for tuning or switching an ultrahigh frequency circuit which may be controlled from a remote position.

A further object of my invention is to provide a new and improved apparatus for tuning or switching an ultra-high frequency circuit in which no mechanical changes in the guides for electromagnetic waves are involved.

A still further object of my invention is to provide a novel, electrically operated apparatus for tuning or switching an ultra-high frequency transmission-line circuit.

My invention arises from the realization that if an electromagnetic wave, for example a plane Wave, is incident on a planar region containing essentially free electrons, some of the energy of the WaVeis reflected at the planar region, Consequently, only a portion of the incident energy is transmitted, into the region. The amount of the wave energy which is reflected is proportional to the electron density up to a calculablelimiting value of density. With an electron density greater than the limiting value, the region containing the electrons acts somewhat like a metal in that the field within it is rapidly damped out, and the incident wave is entirely reflected.

Within the range of electron densities for which the energy reflected is proportional to the density, the effect of the electrons is to reduce the dielectric constant of the region. Thus, thereflection may be considered asthat produced be- 3 Claims. (Cl. 17844) tween two regions of different dielectric con stants. I

'Of course, if the region containing essentially free electrons has a finite thickness, the electromagnetic wave also has a reflected component at the second interface, as well as at the first interface. The net effect of the combined reflected components of the first and second interfaces for any given density depends upon the thickness of the regioncontaining the free electrons measured inwavelengths in the region. If the thickness is an odd multiple of a quarter wave length, the reflection is at a maximum. Of course, with increasing electron density, the wave length in the region increases, so it is not possible to achieve the maximum reflection at all densities with a given thickness'of region. However, any value of reflection up to complete reflection may be achieved by varying the electron density alone.

In accordance with my invention, I propose to introduce a tube into a'transmission line for electromagnetic waves. A portion of the tube is posi-' tioned in the path of the electromagnetic waves, with the walls thereof in the path of the waves constructed of a material permitting the waves to pass therethrough. Means are then provided to establish essentially free electrons within the portion of the tube in the path of the electromagnetic waves and to control of the electron density and thereby control the amount ofwave energy which is reflected.

To establish essentially free electrons within the portion of the tube in the path of the waves, the tube may be filled with a suitable gas, vapor or gaseous mixture, such as neon, and a glow discharge initiated in said portion. The electron density may thenbe adjusted by adjusting the flow of current in the glow discharge. The use of a glow discharge in this manner has several distinct advantages. The glow discharge enables a high electron density to be achieved with but comparatively little power. In addition, the glow discharge permits the use of a tube having a low Q or a low ratio of the energy stored in the tube to the energy lost per half cycle of the electromagnetic waves. Such a tube is considerably easier to design and manufacture and it does not have to be tuned.

If a switching operation is desired within the transmission line, the electron density is adjusted to a value causing complete reflection of the electromagnetic waves. The means for establishing the free electrons within the tube may then be switched on or off by remote control or the adjustment of the means may be switched from one producing a high electron density within the portion of the tube in the path of the waves to one producing a low electron density. As a result, the supply of energy through the transmission line is switched on or oil.

If it is desired to effect a gradual change in the amount of energy reflected by the tube, the electron density may be gradually varied. The variation in the actance introduced by the tube in the transmission line, It has the same elTect as mechanically changing the wave guide interior by plugs, screws and irises.

The features which I consider characteristic of my invention are set forth with more particularity in the appended claims. The invention itself, however, with respect to the arrangement and operation thereof, together with additional objects and advantages, may best be understood from the following description of specific embodiments as illustrated in the drawing, in which:

Figure 1 discloses my invention arranged to effect a switching operation in a hollow wave guide transmission line; and

Fig. 2 illustrates my invention as employed to provide an adjustable reactance in a section of hollow wave guide.

, As shown in Figure 1, a hollow wave guide 1 is provided to guide ultra-high frequency electromagnetic waves. The wave guide I may be rectangular in cross-section, and has an opening at 9 in the top wall thereof through which a tube 3 is mounted. The tube I3 is preferably circular in cross-section and has an anode plate l5 resting on the bottom wall I1 of the wave guide I. A pin I9 is mounted on the bottom of the anode plate l5, and extends through a small .A cathode plate 2| is mounted within a vertical cylindrical member 23 of the tube near the plane ofthe top wall I of the wave guide and the bottom of the cylindrical member 23, and is parallel to the anode plate I 5. An insulating cylinder 24 separates the anode plate l5 and the A filament 25 is mounted within the upper part of the cylindrical member 23 above the cathode plate 2|. The leads 21 and 29 of the filament extend outside the tube l3 through a pressed glass seal 3|. The entire tube l3, including the chamber formed between seal 3| and cathode plate 2| in which the filament is mounted, and the chamber formed between the anode and cathode plates l5 and 2|, is filled with a suitable gas vapor or gaseous mixture, such as neon, and sealed off.

As described hereinafter, the cathode plate 2|;

electron density varies the re-- electron density ents e len choke y gve the his 33 and rs xtending upwar he hollow nde ave uide 1 a distani top all r the W Va length. The elemen a,rter wale and from the cyliri? ed irom'each diameter of the outer p and the mber st a little less than the w1dth \t 5 may be an of the rectangular wave gu m or long W A voltage divider 31 is c. J a source of direct-current PQtBMYCBQ Z EQSS a battery 39. The negative termina. i 'd is connected to one of the filament W the other lead 29 being connected throligi madly open contactor 4| of a push button m 43 to a first intermediate tap 45 on the d" en general form e more positive than the first, is connected throu i another normally open contactor 49 on pus button switch 43 to the supporting the cathode plate 2|. A third intermediate tap 5| on the divider, more positive than either the first or second taps, is connected through another normally open contactor 53 on the push button switch 43 to the anode plate l5. When the push button switch 53 is open, the

tube |3 does not effect any substantial reflection of energy, and the electromagnetic waves pass through the wave guide 1. V

When the push button switch 43 is closed, cur.- rent fiows through the filament 25 and, as the cathode plate 2| is more positive than the filament 25, a low discharge is established between the filament and the cathode plate. At the same time, the anode plate I5 is more positive than the cathode plate 2|, and as holes 55 are provided in the cathode plate 2|, the cathode plate acts as a virtual cathode, and a glow dischargeiis established between the anode plate |5 and the cathode plate 2|. The gaseous glow discharge in the chamber between the anode and cathode plates i5 and 2| provides essentially free electrons with ahigh in the chamber. By adjusting the positions of the intermediate taps on the voltage divider 31, the current in the glow discharge may be adjusted to provide the high elec-' tron density necessary to effect complete reflection of'the electromagnetic Waves in the wave guide 7. Thus, in changing the push button switch 43 from an open to a closed position, the tube I3 is changed from a condition permitting passage of electromagnetic waves through the wave guide to one preventing passage of the waves.

It is to be noted that while the use of a glow discharge permits the use of a tube having a low Q, such as is illustrated, a tube in which the discharge is efiected within a tuned cavity resonator can be employed if desired. It is also to be understood that, while the use of the filament 25 in cooperation with the perforated cathode plate 2| whereby the cathode plate acts 'as a virtual cathode, enables a fine control of the glow'discharge, such a filament is not absolutely'necessary. Electron emission into the chamber in the path of the electromagnetic waves may be accomplished in various other ways as, for example, by replacing the cathode plate 2| with an actual electron emitting cathode. L Theprovision of a remotely controlled switch.-,

ing arrangement, such asis illustrated in Fig.1, particularly useful in a system wherein a plucylindrical member 23 tuning efiects.

rality of wave guides are to be supplied from a single source of electromagnetic waves at different predetermined times. A tube may then be interposed in each wave guide and the glow discharges in all of the tubes controlled from a single commutator element to permit passage of power through different wave guides at selected times.

A tube as described, with means for varying the electron density may be used in several ways. One of the principal uses is the incorporation of such a tube in front of an end plate in a side section or stub of a wave guide, the eiiective position of which plate is to be varied to achieve various Such an arrangement is illustrated in Fig. 2.

In Fig. 2, a main hollow wave guide section 6| is provided through which ultra-high frequency electromagnetic waves are to be transmitted. An auxiliary section 63, known as a side stub, is connected to and branches out from the main wave guide section 6!. The end of the side stub 63 is closed by an end plug or plate 65. It is well known that the circuit may then be tuned by varying the efiective position of the end plate 65.

A tube I3, similar to that shown in Fig. l, is inserted in the side stub 63 in exactly the samemanner as the tube is mounted in the wave guide section 1 of Fig. 1. The connection of the fila ment 25, cathode plate 2| and anode plate l5 to the voltage divider 31 is the same as illustrated in Fig. l but with the push button switch 43 omitted. In addition, a hand-switch B1 is inserted between the voltage divider 3! and the battery 39. With the switch 61 closed, the electron density Within the chamber in the path of the electromagnetic waves may be varied by varying the positions of the intermediate taps. Preferably, taps 45 and 4'! remain stationary with a glow discharge established between the filament 25 and the cathode plate 2| and tap 5! is adjusted to vary the current in the glow discharge between the cathode plate 2| and the anode plate 25 and thereby vary the electron density in the path of the electromagnetic waves. In varying the electron density, the reactance introduced into the side stub 63 is likewise varied. This, in effect, varies the effective position of the end plate 65 and permits various tuning effects to be achieved.

It is to be understood that to obtain satisfactory operation of the apparatus, the amplitude of the field and the pressure of the gas within the tube are preferably both suificiently low so that the energy gained by the electrons from the field does not cause them to make an appreciably greater number of collisions, either elastic or inelastic. Consequently, the apparatus is particularly suitable for operation in low-level circuits,

such as in receiver lines of radar systems or other circuits where the source of electromagnetic energy is at a low level.

Although I have shown and described preferred embodiments of my invention, I am aware that the principles thereof may be applied to several other modifications. I do not intend, therefore to limit my invention to the particular apparatus illustrated.

I claim as my invention:

1. In an electrical system, a hollow wave guide for guiding electromagnetic waves, a tube interposed in said wave guide and including a chamber positioned in the path of said waves, said chamber being filled with gas and comprising an anode plate positioned at one side of said wave guide, a cathode plate having openings therethrough positioned at the other side of said wave guide and insulating walls separating said plates and extending across the path of said waves, said walls being of a material through which said waves may pass, said tube also including a second gas-filled chamber adjacent said cathode plate and a filament mounted within said second chamber, means for establishing a difference in potential between said filament and cathode plate to eiiect a glow discharge therebetween, and means for establishing a difierence in potential between said cathode plate and said anode plate whereby some of the free electrons from said second chamber pass through the openings in said cathode plate and a glow discharge is efiected in said first chamber.

2. In an electrical system, a hollow wave guide for guiding electromagnetic waves, a tube interposed in said wave guide and including a chamber positioned in the path of said waves, said chamber being filled with gas and comprising an anode positioned at one side of said wave guide, a metal plate having openings therethrough positioned at the other side of said wave guide and insulating walls separating said anode and plate and extending across the path of said waves, said walls being of a material through which said wavesmay pass, said tube also including a second gas-filled chamber adjacent said plate and a filament mounted within said second chamber, first means for establishing a difference in potential between said filament and cathode plate to efiect a glow discharge therebetween and second means for establishing a difiference in potential between said plate and said anode whereby some of the free electrons from said second chamber pass through the openings in said plate and a glow discharge is efiected in said first chamber to reflect wave energy, said second means including means for varying the magnitude of the potential difference between said anode and plate thereby to vary the amount of energy reflected.

3. In an electrical system, a hollow wave guide for guiding electromagnetic waves, a tube interposed in said wave guide and including a chamber positioned in the path of said waves, said chamber being filled with gas and comprising an anode positioned at one side of said wave guide, a metal plate having openings therethrough positioned at the other side of said wave guide and insulating walls separating said anode and plate and extending across the path of saidwaves, said walls being of a material through which said waves may pass, said tube also including a second gas-filled chamber adjacent said plate and a filament mounted within said second chamber and means for establishing potential differences between said filament and plate and anode whereby a glow discharge is produced in said second chamber with some of the free electrons therefrom passing through the openings in said plate and effecting a glow discharge in said first chamber, said means including means for varying the potential differences thereby to vary the amount of energy reflected.

SIDNEY KRASIK. 

